In recent times there has been a proliferation of single-use syringe designs which incorporate shields that can be moved to a forward position to shield the needle after use. In most instances, the shield is locked in the forward position after use to prevent multiple uses of the syringe and/or to prevent inadvertent needle-stick injury.
Examples of syringe designs incorporating shields can be found in U.S. Pat. No. 5,584,818 to Morrison, U.S. Pat. No. 5,492,536 to Mascia, U.S. Pat. No. 5,527,294 to Weatherford, U.S. Pat. No. 5,591,138 to Vaillancourt, U.S. Pat. No. 6,099,504 to Gross, U.S. Pat. No. 4,820,275 to Haber, U.S. Pat. No. 5,269,761 to Stehrenberger, U.S. Pat. No. 5,562,626 to Sanpietro, U.S. Pat. No. 4,863,434 to Bayless, U.S. Pat. No. 4,985,021 to Straw, U.S. Pat. No. 5,057,079 to Tiemann, U.S. Pat. No. 5,057,086 to Dillard, U.S. Pat. No. 5,092,851 to Ragner, U.S. Pat. No. 5,201,720 to Borgia, U.S. Pat. No. 5,215,534 to De Harde, U.S. Pat. No. 5,215,535 to Gettig, U.S. Pat. No. 5,222,945 to Basnight, U.S. Pat. No. 5,290,256 to Weatherford, U.S. Pat. No. 5,312,372 to De Harde, and U.S. Pat. No. 5,360,408 to Vaillancourt.
Most of these shielded-syringe designs are provided to the user with the shield in the retracted position and thus some triggering or manual manipulation of the shield is required to release the shield to the forward position after use. In many designs, the movement of the shield to the forward position after use is assisted by a spring.
Only a few of these known designs are provided to the user with the shield initially in the forward position. In these cases, it is necessary for the user to manipulate some form of release mechanism to enable the shield to be moved to the rearward position to expose the needle for use, and after use it is again necessary to manipulate some form of release mechanism to release the shield to the forward position. Again, many of these designs incorporate a spring which biases the shield to the forward position.